This application is based on application No. 018233 filed in Japan on Jan. 27, 2000, the content of which incorporated hereinto by reference.
The present invention relates to a method of displaying the full-charge-state of a rechargeable battery, and more specifically to a method of displaying the-full-charge-state not at the time when the battery is fully charged but a predetermined period of time later from the full-charge-state.
As a battery undergoes charging, the battery temperature rises. The battery temperature rises as charging operation comes closer to completion, and it rises sharply after the full-charge-state is reached because the charging current is consumed as heat loss heating the battery after the full charge state.
FIG. 1 is a graph depicting how the temperature rises during charging. As shown in the figure, the battery temperature continues to rise after charging current is shut off when the full charge is reached. The phenomenon is caused by the fact that heat transfer from inner portion to the outer portion of the battery requires a certain period of time. Since the surface temperature of a battery continues to rise as shown in FIG. 1 even after the full charge-state is reached, the battery user often finds the battery too hot when he removes the battery from the battery charger following the full charge sign given at the time of full-charge. The surface temperature becomes especially high in case of fast charging where stronger charging currents are supplied. The standardized battery such as U1-U4 battery which has a metal casing with no outer cover or a thin layer of covering is easier to get higher surface temperature. The drawback of the battery charger making the battery user uncomfortable from excessive heat is eliminated by a method of displaying the full-charge-state after a delay time, i.e. displaying the full-charge-state a predetermined time after the battery is fully charged.
The longer the delay time, the lower the surface temperature at the time when full charge display appears. However, since the method retards the display of full charge, it is not capable of quickly displaying the full-charge-state for the user. The drawback will be eliminated by using a shorter delay time period. However, as the delay time period is shortened, the battery surface temperature increases, making the user feel uncomfortable when handling the battery.
Thus, protecting the user from excessive heat of the battery conflicts with quickly displaying of a full-charge-state.
The present invention has been completed as a result of intensive study conducted by the inventors about how battery, temperature rises after the full charge is reached. The present invention is based on the fact that the rate of temperature rise varies depending on the charging process. Therefore, the main objective of the present invention is to provide a method of displaying full charge state of a battery while keeping the battery temperature low.
The above and further objectives and features of the invention will more fully be apparent from the following detailed description with accompanying drawings.
The method of the present invention of displaying the full charge involves displaying the full-charge-state with a delay time period after the full-charge-state is detected. The method of the present invention of displaying full-charge-state resides in that in displaying the full-charge-state, a longer delay time period is selected for a rechargeable battery which has been charged with a shorter charging time.
According to the above-mentioned method of displaying the full-charge-state, full charge display can be performed with optimum delay time for the battery being charged, while the battery temperature is kept low. The method of the present invention of displaying the full charge involves displaying the full-charge-state with a longer delay time after the full-charge-state is detected for a battery having a shorter charging time which has a higher temperature rise on one hand, and displaying the full-charge-state with a shorter delay time for a battery having a longer charging time which has a lower temperature rise after the full-charge on the other hand.
According to the present method, the full-charge-state is displayed with a longer delay time for a battery having a shorter charging time, without causing substantial inconveniences to the use of the battery because the delay time is negligible as compared with the charging time. On the other hand, for the battery which requires a longer charging time, fill charge is displayed with a shorter delay time, thus enabling quick display of the full-charge-state after the full charge is detected.
The method of present invention of displaying the full-charge-state employs the delay time as a function of the charging time.
The method of the present invention of displaying the full-charge-state is preferably employed for charging Nixe2x80x94Cd or Nixe2x80x94MH batteries.
The method of the present invention of displaying the full-charge-state employs a charging current of 0.5-4C.